Generally, a plasma display panel (PDP) is a device that displays an image including characters or graphics by emitting phosphor using UV light at 147 nm emitted upon electrical discharge of an inert gas mixture comprising He+Xe, Ne+Xe, or He+Ne+Xe, etc. Specifically, a PDP is a device causing self-luminescence due to an electrical discharge phenomenon in an electrical discharge cell that is formed in the shape of a matrix between an upper substrate having a scan electrode and a sustain electrode and a lower substrate having an address electrode.
The PDP is advantageous, because it can reproduce natural colors using self-luminescence, can assure a wide viewing angle of 160° or more, and can have a large screen, and is also receiving attention for use as a typical flat display device along with LCDs according to the recent trend toward decreased thickness and weight of a display device. However, the PDP suffers because it requires much higher power consumption than conventional CRT display devices, and thus electromagnetic waves and near infrared noise signals are more strongly emitted from the PDP set, compared to those of CRT display devices.
Electromagnetic waves, which affect the human body or other electronic apparatuses, need to be restricted to a predetermined level or less. Further, the near infrared noise signals occurring from the PDP may negatively affect the operation of wireless telephones or remote controllers. Therefore, the PDP requires a shielding structure different from that of the CRT display device as a structure for shielding electromagnetic waves or noise signals, realization of which is the most important technical task.
In order to efficiently shield such electromagnetic waves and near infrared noise signals from the PDP, as shown in the cross-sectional structure shown in FIG. 1, a PDP filter 20 is mounted over the entire surface of a PDP module 50 of a PDP 100. The PDP filter 20 is formed by aligning and attaching one or more functional layers to the upper surface or lower surface of a transparent substrate 22 made of acryl or reinforced glass or of the PDP module, as shown in the cross-sectional structures of FIGS. 2 to 7. The thick line of FIGS. 2 to 7 shows the portion that is silver printed or attached with conductive tape.
As the functional layers constituting the PDP filter 20, there is at least one film selected from the group consisting of an anti-reflection layer 21, an electromagnetic wave-shielding layer 23, a color control layer 24, and a near infrared shielding layer (not shown). The PDP filter 20 composed of such functional layers should be transparent since it is mounted to the front surface of the PDP 100.
The functional layers constituting the PDP filter 20 are laminated while variously changing the lamination sequence, as necessary, in order to exhibit inherent functions of respective layers. The functions of respective layers are as follows. The anti-reflection layer 21 functions to prevent reflection of external incident light to the outside in order to increase the contrast of the PDP 100. The electromagnetic wave-shielding layer 23 functions to shield electromagnetic interference (EMI) occurring in the PDP module 50, which is then grounded to the back cover of the PDP 100 for subsequent electrical discharge. The near infrared shielding layer (not shown) functions to shield near infrared rays at about 800˜1000 nm emitted from the PDP module 50 to prevent the emission of near infrared rays of a predetermined level or more, so that signals, such as remote control signals, which are controlled using infrared rays at about 947 nm, are transferred normally. The color control layer 24 functions to control a specific color using included red (R), green (G) and blue (B) dyes. Moreover, since the electromagnetic wave-shielding layer 23 and the near infrared shielding layer (not shown) are based on a similar shielding principle, either one of the two layers may be formed so as to simultaneously exhibit two functions.
The PDP filter composed of respective functional layers is manufactured by cutting one or more functional layers to a predetermined size and then attaching them to each other, as necessary. As shown in the cross-sectional structures of FIGS. 2 to 7, the conventional PDP filter has unequal cross-sectional widths of the functional layers due to the presence of the electromagnetic wave-shielding layer 23.
The electromagnetic wave-shielding layer typically contained in the PDP filter is specifically described below. The electromagnetic wave-shielding layer may be classified into a metal mesh type and a transparent conductive film type, depending on the kind of film used. Although the PDP filter having a mesh type electromagnetic wave-shielding layer exhibits excellent electromagnetic wave-shielding effects, it reduces transparency and causes image distortion. Further, since the mesh itself is expensive, a product price is undesirably increased.
Hence, in order to substitute for mesh type, a PDP filter having a transparent conductive film type electromagnetic wave-shielding layer such as ITO layer has been widely used. The transparent conductive film type electromagnetic wave-shielding layer is in a multilayered thin film form, in which metal thin films and high-refractive transparent thin films are alternately applied, and preferably alternately applied three times or more, and a high-refractive transparent thin film is further applied as the uppermost layer. The metal thin film is formed of silver (Ag) or alloy composed mainly of silver, and has surface resistance of 3 Ω or less and visible light transmittance of 50% or more.
The structure of the PDP filter including the conventional transparent conductive film type electromagnetic wave-shielding film is shown in FIG. 8. The edge portion of the surface of the conventional transparent conductive film type electromagnetic wave-shielding film 70 has an exposed portion 71 for electrical grounding. The exposed portion 71 may be silver printed or attached with conductive tape in order to prevent an increase in resistance due to oxidation. The exposed portion 71 is connected with a filter supporter 30 through contact with a ground pin 170 to realize electrical grounding to the back cover, or may be directly grounded to the corresponding surface of the PDP, thereby grounding the electromagnetic waves.
That is, since the transparent conductive film type electromagnetic wave-shielding film 70 as one constituent of the PDP filter 20 should have the exposed portion 71 for grounding, other functional layers that are attached to the upper surface of the electromagnetic wave-shielding film 70 should be cut to be smaller than the electromagnetic wave-shielding film 70 so that the exposed portion 71 of the electromagnetic wave-shielding film 70 is exposed outside the laminated structure of the PDP filter. Thus, the conventional PDP filter has a limit in that the cross-sectional widths of the functional layers cannot be completely equal to each other, as shown in FIGS. 2 to 7.
Consequently, due to the cross-sectional structure of the PDP film mentioned above, each of the PDP filter is manufactured by aligning and attaching one by one the functional films, each smaller than the size of the transparent conductive film type electromagnetic wave-shielding film. However, such a manual process complicates manufacturing processes, and a roll-to-roll process (continuous manufacturing process) cannot be implemented, and thus mass production is impossible to realize, resulting in decreased productivity.
The anti-reflection film may be manufactured by forming the high-refractive transparent thin film and the low-refractive transparent thin film on the transparent substrate. That is, in the structure of the anti-reflection film, the low-refractive transparent thin film should be positioned as the uppermost layer, and the high-refractive transparent thin film should be positioned therebeneath.
With the intention of manufacturing a light and thin PDP in the related art, various attempts have been made to manufacture a PDP filter through integration of the transparent conductive film type electromagnetic wave-shielding film and the anti-reflection film into a multilayered structure using the transparent substrate in common. For example, Japanese Patent Laid-open Publication No. Hei. 11-74683 discloses a method of manufacturing a PDP filter comprising interposing an electromagnetic wave-shielding film between two transparent substrates, attaching an anti-reflection film to one surface of the resulting substrate, and sequentially laminating a near infrared shielding film and an anti-reflection film on the other surface of the resulting substrate. In addition, Japanese Patent Laid-open Publication No. Hei. 13-134198 discloses a method of manufacturing a PDP filter comprising sequentially attaching an electromagnetic wave-shielding film and an anti-reflection film to one surface of a transparent substrate, and then attaching a near infrared shielding film to the other surface of the transparent substrate.
The above conventional methods may realize relatively light weight and thinness. However, even though the laminated structure is formed using the transparent substrate in common, the conventional methods are disadvantageous because individual functional films should still be manufactured by separately forming the electromagnetic wave-shielding layer or anti-reflection layer on the transparent substrate. Further, limitations are imposed on further decreasing the number of processes of separately manufacturing respective functional films or the number of laminated layers.